The present invention relates to sound outputting devices to demodulate sound information which have been subjected to delta modulation (DM) or adaptive delta modulation (ADM).
Electronic devices are known which store digitized sound messages and reproduce the stored messages when required.
Various systems which digitize sound information are known. The DM and the ADM which is a modified delta modulation have the advantage of requiring less than a quantity of data required in the digitization of sound information than other digitizing systems which convert a sampled analog sound value to a digital value each time such sampling is made. Thus, when sound information is stored in a small-sized electronic device or the like, these DM and ADM are used in many cases.
The DM system compares the current sampled sound data value with the last sampled value, converts the former sound data to digital data "1" or "0" depending on whether the former value data is larger or smaller than the latter data value, and holds a one-bit data value at each sampling.
The ADM system gives predetermined different weights to the digital value "1" and "0" obtained by the ADM or DM. That is, the added or subtracted value .DELTA.M (.gtoreq.1) is incremented by one at each sampling each time "1" or "0" appears successively while when either "1" changes to "0" or "0" changes to "1", "1" is subtracted from the .DELTA.M value to thereby obtain the current data.
For example, when the digital data value changes as follows: EQU 1, 1, 1, 0, 0, 0, 1.
The added or subtracted value .DELTA.M changes in the ADM as follows: EQU +1, +2, +3, -2, -3, -4, +3.
Therefore, the sampled amplitude value of the sound information is as follows: EQU 1, 3, 6, 4, 1, -3, 0.
As just described above, ADM differs more or less from DM in the significance of the digital data value. Also in the ADM, the digital data for each sampling operation can be expressed in one bit.
In order to decode and reproduce the sound information which has been subjected to ADM, clock generating means synchronous with ADM sound information received from a source of sound information, analog reproducing means, sound outputting means, power supply means and reproducing means are required.
Permanent provision of these means on an electronic device such as an electronic notebook would make it difficult to miniaturize the device as well as increase at least the cost. When a sound outputting device provided with these means is provided optionally for the electronic notebook, control means and data buses are required for providing an interface function between the electronic notebook as the device proper and the sound outputting device in addition to the above respective means.